1. Technical Field
The present invention relates to a method of manufacturing an MEMS device, and more particularly, to a manufacturing process for adjusting the structural size of an MEMS structure.
2. Related Art
MEMS (Micro Electro Mechanical Systems) relate to one of the technologies for forming micro structures. For example, MEMS relate to technology for producing a delicate electromechanical system of a micron order or such products. Generally, semiconductor chips have a circuit structure that is a two-dimensional pattern by manufacturing an electronic circuit by stacking thin films such as a silicon film, an oxidation film, and a metal film on a silicon substrate. However, when the technology for manufacturing the semiconductor chip, that is, semiconductor manufacturing technology is used in the MEMS, a leaf spring, a mirror, a rotation shaft, and the like of micron sizes are formed by forming a thin film on a substrate and by partially separating the thin film from the substrate by performing an etching process. Accordingly, an MEMS structure has a three-dimensional structure and has a movable portion at least in a portion thereof.
As one of the fields for which the MEMS have attracted attention, there is a field of communication technology for configuring cellular phones or the like. In the cellular phones, many components such as a filter, an antenna switch, a transmitter and receiver switch, and the like other than an LSI are assembled. When utilization of multiple bands that use Bluetooth or wireless LAN is implemented, the number of inactive components such as an antenna shift switch and a band shift switch is increased. Thus, in order to implement miniaturization and power saving, it is a most effective countermeasure to decrease the number of components that are housed in one semiconductor chip. According to this countermeasure, there are additional advantages in that wiring is shortened, improvement of performance of MEMS components such as strength for noise and low loss can be acquired due to operation of the MEMS component performed in a mechanical manner. In addition, by using the semiconductor, integration of the MEMS components with typical existing constituent components such as integration of the MEMS components with an LSI by using semiconductors can be achieved. As an example of the above-described method of manufacturing the MEMS device, for example, there is technology disclosed in JPA-2008-114354.
As described above, the MEMS has various advantages. However, since the structure has a micro size, a deviation in the manufacturing process much affects the operating characteristics. In addition, in order to acquire high-performance operating characteristics that are uniform, various adjustment methods are necessary. For example, an MEMS resonator outputs signals having a predetermined frequency, and the frequency characteristics, for example, the operating frequency (resonance frequency), need to be within an allowed range that is regulated. As methods of adjusting the frequency characteristics, a method of increasing or decreasing the operating frequency by changing a driving voltage (DC bias voltage) (see S. Chowdhury, M. Ahmadi and W. C. Miller. “A Closed-Form Model for The Pull-in Voltage of Electrostatically Actuated Cantilever Beams”, Journal of Micromechanics and Microengineering, 2005, pp. 756-763, vol. 15), a method of changing the physical properties or the size of the material by heating a movable portion which vibrates by allowing a current to flow through it (see JP T-A-2007-535275), a method of depositing a material in a movable portion (see Daphne Joachim, Liwei Lin, “Characterization of Selective Polysilicon Deposition for MEMS Resonator Tuning” Journal of Micromechanical Systems, April 2003, pp. 193-200, vol. 12, No. 2, IEEE), and the like have been proposed.
However, according to the above-described method of changing the operating frequency by changing the driving voltage, the range in which the operating frequency can be changed is limited. Accordingly, there are cases where adjustment cannot be performed. In addition, there is a problem that adjustable devices are limited to devices in which the operational aspects of a vibrator or the like depend on a driving voltage.
In addition, according to the above-described method using heating due to a current, since the method depends on the constituent material of a structure, there are cases where sufficient adjustment cannot be performed. In addition, there is also a problem in that the operational aspects may be changed such as a change in the vibration mode due to a partial change of the movable portion or the like.
In addition, according to the above-described method of depositing a material in the movable portion, the operational aspects may be changed, similarly to the above-described method, like a change in the vibration mode or the like by attaching a material in a part of the movable portion.